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CHARGE SEPARATION IN TRANSITION METAL AND QUANTUM DOT
SYSTEMS
by
Diana Masayo Suffern
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
May 2011
Copyright 2010 Diana Masayo Suffern

Ultrafast pump-probe and pump-broadband probe spectroscopy and timecorrelated-single-photon-counting (TCSPC) techniques are used to study two different systems that undergo charge separation upon UV excitation. The first system is a model transition metal coordination compound, aqueous tribromocuprate(I) anion (CuBr₃²⁻). CuBr₃²⁻ has an absorption band centered at 280 nm, assigned as charge-transfer-tosolvent (CTTS) since resonant excitation in this band produces solvated electrons as reported in the literature. However, unlike most CTTS systems where ejection occurs on a femtosecond timescale, electron ejection has previously been reported for CuBr₃²⁻ to occur over nanoseconds, and the anion also undergoes intersystem crossing from its initially populated CTTS state to a triplet state. The spectral and kinetic features obtained in the current ultrafast experiments reveal that UV excited CuBr₃²⁻ has complex femtosecond/picosecond excited state dynamics and a surprisingly small quantum yield of prompt solvated electrons via its charge-transfer-to-solvent (CTTS) state. Analysis of data from a combination of broadband, low intensity, and photon counting experiments contributes to a proposed kinetic model, which includes some of the transient species reported for nanosecond flash photolysis. Aside from transient kinetics, an oscillatory signal was analyzed and it is determined that a vibrational wavepacket on the potential energy surface of the CuBr₃²⁻ CTTS state is launched via resonant excitation by the pump pulse. This vibrational coherence survives intersystem crossing into a CuBr₃²⁻ triplet state.; A second set of systems studied include CdSe/ZnS, CdSe, and CdTe quantum dots (QDs), where charge separation to an electron – hole pair precedes emission. These QDs in the presence of β-mercaptoethanol (BME) are characterized by time-correlatedsingle-photon-counting (TCSPC) and it is observed that BME has an effect on the photoluminescence lifetimes in all three of these QD systems. Varying the nature of the QD surface and also the band gap energy of the QD changes the luminescence lifetime of the QD – BME system. It is proposed that the presence of BME leads to competition between two mechanisms: surface passivation of Cd electron traps resulting in photoenhancement, and hole transfer between Se and BME resulting in luminescence quenching.

CHARGE SEPARATION IN TRANSITION METAL AND QUANTUM DOT
SYSTEMS
by
Diana Masayo Suffern
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)
May 2011
Copyright 2010 Diana Masayo Suffern